Unmanned aerial vehicles (UAVs) have been developed for a large array of tasks. One such UAV task is for aerial reconnaissance. In UAV reconnaissance aircraft, a payload consisting of one or more cameras, and possibly one or more gimbaled supports for the cameras, might preferably extend below the fuselage and/or wing of the aircraft for maximum unimpeded viewing during flight. This configuration potentially puts the cameras and gimbals in harm's way during landing, particularly for payloads that are sensitive to high vibration and impact loads.
Larger UAVs tend to have a significant range (distance they can travel), and are typically provided with standard aircraft take-off and landing facilities. These aircraft do not typically have to take off and land in combat settings in which the visual exposure of the ground crew may be life threatening. Moreover, larger UAVs are naturally required to have landing gear configurations that are structurally size appropriate to their aircraft, which may be significantly larger than the payload size requirements for a reconnaissance payload. Thus, the landing gear configuration for larger UAVs tends to be such that the payload is structurally supported and protected during landing. Moreover, the cost of such an aircraft is generally large in comparison to the cost of its payload, so the payload may be made structurally tolerant without significantly increasing the overall cost of the combined aircraft and payload.
Smaller UAVs are often used in military field situations, in which little or no room is available for rolling landings, and in which precision landings are important to limit the exposure of field personnel to enemy fire. Precision landings are also useful when attempting to land the aircraft in a limited location such as a rooftop. Likewise, in civilian applications, similar needs may be found in urban settings for which only a limited ground space is controlled during an emergency situation, such as near a burning building. For smaller UAVs, a number of adaptations have been used to protect low-hanging payload integrity during landing. One adaptation is to use payloads having high structural integrity (such as using only sturdy, non-gimbaled cameras) to provide for payloads that are tolerant to the high vibration and impact loads that occur when the payload strikes the ground.
For example, the Raven® UAV, with a wingspan over 4 feet, provides low-altitude surveillance and reconnaissance intelligence for both military and commercial applications. Such an aircraft can be configured with a cushioned landing pad (in place of landing gear) that allows provide for an extremely short-field landing (at the expense of much higher landing loads). The relatively accurate short field landing capability does help protect ground crews from the possible dangers of open exposure (e.g., in military situations).
This aircraft may also be equipped with a payload of a group of robust stationary cameras that can handle the high landing loads. Nevertheless, high resolution cameras of such structural integrity can be very expensive. Given that smaller UAVs are significantly less expensive that large UAVs, providing a group of highly expensive cameras to a small UAV can add significantly to the cost of the aircraft. Alternatively, such an aircraft can be configured with the entire payload being gimbaled not only for a wide field of viewing, but also such that it swings up into the fuselage prior to landing. While this may be effective to reduce the landing loads on the payload, the gimbal mechanism adds significant weight, and the need to fit it within the fuselage limits the size and shape of the payload.
Another known adaptation for smaller UAVs is to use a parachute to land the aircraft. In such a maneuver, the engine is stopped and the parachute is deployed while the aircraft is in the general vicinity of the desired landing location. Moreover, the parachute can be attached to the bottom of the aircraft to provide for the aircraft to land not on its lower surface, but rather on its upper surface (which can include landing struts to support the vehicle during a vertical-decent landing). If the timing of such a deployment is accurate, the winds are cooperative, and the parachute both successfully deploys and successfully inverts the aircraft without tangling in part of the aircraft structure, then a landing within a limited field location with limited landing loads might be possible.
Nevertheless, this involves surrendering flight control once a parachute is deployed, and thus greatly reduces the likelihood of a precise landing location. Also, a parachute landing is also difficult to “call-off” if landing the aircraft is no longer desired, the landing trajectory is incorrect, or the landing site is no longer cleared. Such issues could be extremely important in a situation where landing location is important, such as needing to land an aircraft on a rooftop or near a protected enclosure for ground personnel. Moreover, the skill level required to properly estimate a landing location in situations of varying wind speed and direction conditions might be higher than the skill level otherwise required for use of the aircraft.
Accordingly, there has existed a need for an unmanned vehicle capable of accurate landings with a load sensitive payload that extends significantly from the bottom of the aircraft. Preferred embodiments of the present invention satisfy these and/or other needs, and provide further related advantages.